A typical turbomachine, such as a gas turbine engine used in aircraft applications, includes a compressor section, a combustion section, and a turbine section. A flowpath for working fluid extends axially through the turbomachine and sequentially through each section. The compressor section includes a plurality of airfoil shaped blades disposed on rotating disks. The blades extend radially through the flowpath and interact with the working fluid. The compressor section adds energy, in the form of increased momentum, to the working fluid as it is flowed through the compressor section. The combustion section mixes fuel with the working fluid and burns the mixture to add more energy to the working fluid. The products of the combustion process are then expanded through the turbine section to transfer energy from the working fluid to the turbine section. The turbine section includes a plurality of airfoil shaped blades which extend from rotating disks and through the flowpath. A portion of the energy removed from the working fluid by the turbine section is then transferred to the compressor section via rotors connecting the compressor disks and the turbine disks. This energy is then used to compress incoming working fluid in the compressor section.
One result of the combustion process is an increase in the temperature of the working fluid flowing out of the combustion section and through the turbine section. The energy added by the combustion process is directly proportional to the increase in temperature of the working fluid. The allowable temperature, and consequently the output of the turbomachine, is limited by the temperature characteristics of the turbine section. Extremely high temperatures can adversely affect the structural integrity of the components within the turbine section. Highly stressed components, such as turbine disks, must be maintained below acceptable temperature limits which depend upon material properties. In addition, rotating seals, which block working fluid from escaping the flowpath within the turbine section, must be maintained within acceptable temperature limits to ensure proper functioning.
Cooling fluid is used to protect the components within the turbine section and thereby extend the operating temperature range of the turbine engine. A typical cooling system bleeds working fluid from the compressor section. The bleed fluid is flowed around the combustion section, in order to bypass the combustion process, and into the turbine section.
One means of bleeding fluid from the compressor section is to use a cooling fluid bleed tube known as an anti-vortex tube. The anti-vortex tube bleeds compressed working fluid from a stage of the compressor section. The stage is selected to have an appropriate pressure differential. Pressure differential is the difference between pressure at the selected stage of the compressor and pressure in the region of the turbine section to be cooled. Sufficient pressure differential is needed to ensure an adequate flow of cooling fluid. The anti-vortex tube provides a radially oriented flow passage. The flow passage permits cooling fluid to flow from the compressor through a cavity defined by the separation of the rotor and compressor disks and into a region radially adjacent to the rotor in towards the rotor. The flow passage avoids pressure losses which would normally occur if the cooling fluid were bled directly into the rotating annulus of fluid in the cavity between the compressor disk and rotor. Upon exiting the anti-vortex tube, the cooling fluid, because of its high pressure relative to the fluid within the region of the turbine section to be cooled, travels axially downstream along the rotor. The cooling fluid passes into the turbine section where it provides cooling for turbine section components.
Means for retaining the anti-vortex tube to the compressor disk must accommodate both static load forces and rotational forces resulting from operation of the gas turbine engine. A primary concern is the level stress in the rotating compressor disks. The rotational forces present in the turbomachine result in compressor disks which are highly stressed during operational conditions. Typical retaining means, such as threaded inserts and threaded apertures, cannot be used due to the local stress concentrations associated with the threads. Another concern is foreign object damage to fragile rotating components of the compressor section, such as the rotating blades and rotating seals. Foreign object damage may occur if the retaining means fails and permits portions of the retaining means or anti-vortex tube to enter the flowpath of the working fluid. The failure of the retaining mechanism may result in damage propagating throughout the turbomachine.
The current means of retaining anti-vortex tubes to the compressor disk is to flare the inlet end of the anti-vortex tube. The flared inlet end conforms to the aperture in the compressor disk. A flange, disposed on the tube and in abutting contact with the disk, combines with the flared inlet to provide a clinching force. In effect, the flared portion and the flange clinch the tube to the disk. By using a flared type retention means rather than a threaded type retention means, the local stress concentration associated with threaded apertures is avoided in the compressor disk. In addition, if the flared retention should fail, the flange prevents the anti-vortex tube from entering the compressor section flowpath.
Although the current retaining means has proven satisfactory, there are several limitations to its use. The first is that the flared anti-vortex tube cannot be reused once it has been removed. Upon removal, the tube must be replaced with a new tube which is then flared into place. This represents an increase in cost associated with repair and refurbishment of the turbomachine. A second limitation is that the inlet end of the anti-vortex tube is required to be a flared opening. The opening cannot be modified to produce improved flow characteristics.
The above art not withstanding, scientists and engineers under the direction of Applicants' Assignee are working to develop means for retaining an anti-vortex tube to a compressor disk of a turbomachine.